The gateway to heaven will look a lot like the Gunpowder River in autumn. The chosen few will don chest waders and walk over to Glory Land, and diehard anglers among them can stop and fly-fish in dappled runs and placid pools as long as they like.

They probably will not be rewarded with big fish, because there aren't a lot of big trout in the Gunpowder. They won't catch all that many, either, because while the river holds a sizable population, the trout are wary, experienced and tough to fool. Nor will they get to keep them for the pan, because the best parts of the river are catch-and-release.

But they will surely catch a few, and some will be beautiful beyond measure -- wild, mature, stream-bred browns dressed in buttermilk and gold with brilliant spots of ebony and vermillion. To hold one in your hand even briefly is to touch heavenly perfection.

Okay, okay, pardon me for bubbling over again, but I'm just back from a half-day autumn outing on the Gunpowder and the flowery prose has to get out. I'm still in the thrall.

The Gunpowder tumbles over rock ledges through deeply forested banks just a few miles from downtown Baltimore and has been named one of the 100 top trout streams in the nation by folks who know. That's doubtless an overstatement, given the abundance of spectacular trout water in mountain states out West.

"I'm sure you could find 100 streams that are better," said veteran trout guide Stacey Crossland-Smith, with whom I shared the water last week, "but when you consider accessibility and location, this one is definitely up there."

It is also a remarkable success story. Twenty-five years ago, it was just another mid-Atlantic gully connecting the bottom of Prettyboy Reservoir with the top of Loch Raven Reservoir, Baltimore's main freshwater supply. In 1986, local trout fanciers came up with the idea of regulating the flow out of Prettyboy to encourage trout survival.

It wasn't nuclear physics. With the guarantee of a steady, year-round supply of cool, clear water from the depths of the reservoir, a natural resource sprang to life. A few years of trout stocking provided the seed, catch-and-release regulations on the productive upper stretch from Falls Road up to the dam protected the fish and the rest is happy history.

These days, the Gunpowder rarely gets above the low 60s (Fahrenheit, of course) in water temperature, even in the hottest summer stretches. Anglers joke that it's one of the rare places you can suffer hypothermia and heat exhaustion at the same time.

Brown trout in particular thrive among the Gunpowder's rocks and rills, alongside a few rainbows and brookies. The fish feast on a year-round supply of hatching insects including caddisflies, stone flies, tiny tricorythodes, mayflies and terrestrials such as ants, beetles and inchworms that drop into the water.

You can catch fish on dry flies here, but as in most Eastern waters it often pays to go deep to attract the bigger ones.

Crossland-Smith led the way down a dirt path to the stream from the parking lot on Falls Road, not far from the roaring traffic on Interstate 83. You couldn't hear any traffic noise down in the valley, just the chirping of cardinals and chickadees and the lively chuckle of water over rocks.

He pointed to a favored pool and had me wade in gently. "Now," he said, "we'll just stand here for a few minutes and watch. These fish get enough pressure, they can feel the ripples when an angler steps in. It takes them awhile to settle down."

Sure enough, after a few minutes the trout came back to the surface and resumed slapping and sipping at tiny flies emerging. Crossland-Smith reckoned they were caddis, the most common insects to hatch here, but it turned out later they were mostly small stone flies.

So began the fly angler's process of elimination as we went through the flybox trying to find something to match the hatch. We went larger, smaller, lighter, darker, and tried a pattern that copied the look of a fly rising from the rocky depths to hatch on the surface.

It was slow going. In a less beautiful place that might have proved annoying, but it's hard to get annoyed when you're knee-deep in clear, cool water on a bright autumn day with a breeze in the trees and fish rising all around.

We tied on a size 18 Adams and bang, there he was. Then, as I played around with small fish on the surface, Crossland-Smith put a small white grub imitation on his line, weighed it down with a split shot and dredged it through a fast run just upstream.

On the third or fourth drift, the strike indicator went down and he set the hook on something of consequence. It was a wild, 12-inch brown trout, and when he lifted it from the water, gently cradled in the landing net, it caught the sun just so and took your breath away.

* * *

Someone reading the preceding account might scratch his cheek and say, "Gee, this guy knows a bit about trout fishing." Ha, ha, ha. I'm a tidewater man, more at home with crabs and channel markers than strike indicators and wading staffs. But a good trout stream never lets you down. They are among the purest, prettiest, most interesting natural places you ever will see, whatever your background.

It helps to have a guide when you're new to this stuff and Crossland-Smith is a good one. He's one of six guides booking trips out of Backwater Angler (410-329-6821), a well stocked fly-fishing shop near the river.

Those with some fly-fishing expertise can learn everything they need to know to fish the Gunpowder and 14 other trout streams by getting a copy of the Guide to Maryland Trout Fishing by local anglers Charlie Gelso and Larry Coburn ($19.95, from Falling Star Publishing; e-mail putinpocket@aol.com).

Coburn is giving a free slide show and talk on fall fly-fishing for trout from 11 a.m.-noon next Sunday (Sept. 23) at the Bass Pro Shop in Hanover, Md. (Disclaimer: Yes, Coburn is my No. 1 fishing partner, so I am biased. Still, he knows his stuff.)